1. Field of the Invention
The present invention relates to a real-image type optical finder which includes a relay lens system and which is provided independently from the photographing system.
2. Description of the Related Art
It is well known for a real-image type optical finder to include a positive first lens group, a positive second lens group (relay lens system), and a positive third lens group (eyepiece lens system), in this order from the object side. In this system, a primary image of an object is formed through the positive first lens group, a secondary image is formed through the second lens group which inverts the primary image to attain an erect image, and the secondary image can be viewed through the third lens group.
Further, a real-image type optical finder in which condenser lenses (positive lenses) are provided in the close vicinity of the primary and secondary images, respectively, so as to form an exit pupil at an appropriate position behind the eyepiece lens system, thereby facilitating viewing performance, is also known. However, a problem arises with an increased cost due to the increased number of positive lenses. Also, due to the increase of positive lenses, the Petzval sum becomes large which causes an increased field curvature, causing the periphery of the image to be blurred, making it difficult to attain a high quality image.
Moreover, in order to maintain a long eye relief (the distance between the user's eye and the closest lens surface of the eyepiece lens system), it is necessary for the eyepiece lens system to have a long focal length. However, if the focal length of the eyepiece lens system is lengthened, there is the problem of the size of the entire finder body increasing.